1. Field of the Invention
The present invention relates to a slide device for a vehicle seat that moves an upper rail installed on a seat body in the front-rear direction with respect to a lower rail installed on a vehicle body, thereby allowing the seat body to slide in the front-rear direction.
2. Description of the Related Art
A typical slide device for a vehicle seat is mainly configured with a lower rail that is fixedly installed on a floor of a vehicle body and long in the front-rear direction of the vehicle body, and an upper rail that is coupled to the lower rail so as to be relatively movable and supports a seat body. In this type of slide device for the vehicle seat, when a seat belt acts to hold a passenger to the seat upon a crash or the like, the front portion of the upper rail receives a strong force in the direction in which the front portion of the upper rail is to tilt forward with respect to the lower rail. On the other hand, the rear portion of the upper rail receives a strong force in the direction in which the rear portion of the upper rail is to lift upward off the lower rail.
Japanese Unexamined Patent Application Publication No. 1993-124462, for example, discloses a seat track technology that prevents a sliding portion of the upper rail from departing from the lower rail by inserting the sliding portion of the upper rail to a guiding space formed at the lower rail and extending the upper rail from the sliding portion to the outside through an opening formed at the lower rail, providing an engaging projection projecting outward at the edge of the opening of the lower rail and a regulating protrusion engaging with the engaging projection from the both sides at the upper rail, and regulating widening of the opening by the engagement of the engaging projection and the regulating protrusion.
However, the technology disclosed in Japanese Unexamined Patent Application Publication No. 1993-124462 essentially aims to prevent the sliding portion of the upper rail from departing from the lower rail, and cannot cope with the above-mentioned force applied to the front portion of the upper rail in the forward-tilting direction with respect to the lower rail. If this downward force is intensively applied to the front portion of the upper rail, the lower rail may be bent downward into a convex shape, whereby the front-rear movement of the upper rail may be hindered. In particular, in the case of a so-called three-row seating vehicle, which has three rows of seats in a vehicle compartment in the front-rear direction, if the front-rear movement of a seat body in the second row is hindered, it may be difficult for an occupant seated in the third row to escape quickly. In order to address this problem while ensuring a smooth seat slide operation even upon a frontal crash, the lower rail may be composed of a highly rigid material for example, but the enhancement of the rigidity of the lower rail could cause an increase in weight, a steep rise in cost and the like.